pinctrl: imx: Add imx8dxl driver

i.MX8DXL contains a system controller that is responsible for controlling
the pad setting of the IPs that are present. Communication between the
host processor running an OS and the system controller happens through
a SCU protocol, add support for the SCU based i.MX8DXL pinctrl driver.

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Link: https://lore.kernel.org/r/1585306559-13973-2-git-send-email-Anson.Huang@nxp.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>